In recent years, various thermal insulation coating materials have been proposed for forming thermal insulation coating films that reflect infrared light on surfaces of buildings and roads as one of the increasingly demanding energy-saving measures (for example, see Patent Documents 1 and 2). Coloring of these thermal insulation coating materials may be performed by a technique according to the subtractive color mixing method using a pigment with high infrared-light reflectance, such as titanium dioxide.
Meanwhile, a pigment having infrared-reflective capability may, in nature, generally reflect visible light as well. The selection of pigments in coloring may also be very limited. For example, a coloring pigment with less infrared-light absorption needs to be selected. Further, a dark color system such as black in particular may reduce infrared-light reflectance because of its low content ratio of titanium dioxide in a pigment. Therefore, the above technologies currently cannot be used for applications requiring sophisticated designs such as automobile bodies. In order to make it possible to apply to coating films having sophisticated designs, there have been demands for an infrared-reflective pigment having both high infrared-light reflectivity and high visible-light transmissivity.
As the infrared-reflective pigments such as described above, for example, as pigments which can reflect infrared light, but allow visible light to transmit, proposed are those including transparent electrically-conductive inorganic particulates such as ITO (tin-doped indium oxide) and ATO (antimony-doped tin oxide) (For example, see Patent Document 3), those including nano-sized hexaboride particulates as a heat-ray insulation component (for example, see Patent Document 4), optical coherence pigments with multilayered films of oxides (for example, see Patent Document 5). Heat-ray insulation plates also have been proposed in which titanium dioxide, or inorganic particles such as mica coated with titanium dioxide, which have heat-ray reflective capability, are kneaded in a transparent resin (for example, see Patent Documents 6 and 7).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2002-20647
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2002-320912
Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2001-262016
Patent Document 4: Japanese Unexamined Patent Application, Publication No. 2004-162020
Patent Document 5: Japanese Unexamined Patent Application, Publication No. 2004-4840
Patent Document 6: Japanese Unexamined Patent Application, Publication No. H05-78544
Patent Document 7: Japanese Unexamined Patent Application, Publication No. H02-173060